Meteorologische Zeitschrift (Jul 1996)
On the mesoscale structure of the intra-Alpine precipitation distribution during a typical winter snowfall event
Abstract
Over the period of Feb. 19-23, 1993 several snow storms in Northern Tyrol, Austria, produced a total precipitation distribution very similar to that of climatology, thus allowing to study in detail the typical weather situations leading to winter snowfall. Despite a generally northwesterly upper-level flow, most of the storms moved eastwards across the forelands and the mountain ranges north of the Alpine crest; only one swept across the crest. Observational data are from a very dense network of routine surface stations, rawinsoundings and additional snow depth measurements. Precipitation amounts varied not so much with elevation but more with the location relative to the mountain ranges and their orientation relative to the flow direction (mostly northwesterly for this period). "Virtual topography" comprised of cold air from a back-door cold front that filled the Inntal limited the descent and consequently the drying out of the air en route from the northern mountain ranges to the even higher Alpine crest. Only with virtual topography did the central parts of the Inntal receive substantial precipitation amounts. Without deep cold air in the Inntal, 24 hourly precipitation sums were found to decrease up to a factor of 10 over a horizontal distance of only 5 km downstream of the northern mountain ranges.
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